Iran's elite Revolutionary Guards has vowed to exact "deadly and unforgettable" vengeance for an attack on a military parade that killed 25 people, including 12 of their comrades, as Tehran accused Gulf Arab states of backing the gunmen.
Saturday's assault, one of the worst against the most powerful force of the Islamic Republic, struck a blow at its security establishment at a time when the US and its Gulf allies are working to isolate Tehran.
"Considering (the Guards') full knowledge about the centres of deployment of the criminal terrorists' leaders ..., they will face a deadly and unforgettable vengeance in the near future," the Guards said in a statement carried by state media on Sunday.
Four assailants fired on a viewing stand in the southwestern city of Ahvaz where Iranian officials had gathered to watch an annual event marking the start of the Islamic Republic's 1980-88 war with Iraq. Soldiers crawled about as gunfire crackled. Women and children fled for their lives.
Iranian armed forces members and civilians take shelter. Source: AAP
Islamic State's Amaq agency posted a video of three men in a vehicle who it said were on their way to carry out the attack.
A man wearing a baseball cap emblazoned with what appears to be a Revolutionary Guard logo discussed the impending attack in Farsi in the video. "We are Muslims, they are kafirs (non-believers)," the man says. He adds: "We will destroy them with a strong and guerilla-style attack, inshallah (God willing)."
Iranian soldiers, women, and children lay down and run during a terror attack that occurred at military parade in the city of Ahvaz, southern Iran Source: AAP
Ahvaz National Resistance, an Iranian ethnic Arab opposition movement which seeks a separate state in oil-rich Khuzestan province, also claimed responsibility for the attack.
Neither of them provided evidence.
There has been a blizzard of furious statements from top Iranian officials, including President Hassan Rouhani, accusing Iran's adversaries the US and Gulf states of provoking the bloodshed and threatening a tough response.
Nikki Haley, US ambassador to the United Nations, rejected Rouhani's accusations.
"He's got the Iranian people ... protesting, every ounce of money that goes into Iran goes into his military, he has oppressed his people for a long time and he needs to look at his own base to figure out where that's coming from," she told CNN.
An Iranian soldiers carries a baby as he tries to save a family during a terror attack during a military parade in the city of Ahvaz, southern Iran Source: AAP
Senior commanders of the Islamic Revolutionary Guards Corps (IRGC) have said the Ahvaz attack was carried out by militants trained by Gulf states and Israel, and backed by America. But it is unlikely the IRGC will strike any of these foes directly.
Diplomatic row
Iran also warned the United Arab Emirates over "offensive remarks" attributed to a UAE "political adviser" following the attack.
Oman, Kuwait and Qatar issued condemnations of the attack, while Saudi Arabia and Bahrain had yet to react on Sunday.
The UAE minister of state for foreign affairs, Anwar Gargash, for his part, stressed his country's rejection of acts of terrorism and accused Tehran of a campaign of "official incitement" against the Emirates.
State media initially gave a toll of 29 dead and 57 wounded in the attack, including women and children, but Ahvaz city governor Jamal Alami Neysi said Sunday this was a mistake and put the numbers at 24 dead and 60 wounded.
Their funerals will be held on Monday.
Three attackers were also killed and the fourth died later of his injuries, the armed forces said.
IS had claimed the attack via its propaganda mouthpiece Amaq, and that the attack was in response to Iranian involvement in conflicts across the region.
The Revolutionary Guards accused Shiite-dominated Iran's Sunni arch-rival Saudi Arabia of funding the attackers, while Iran's supreme leader Ayatollah Ali Khamenei also blamed Iran's pro-US rivals.
"A deadly and unforgettable revenge will be exacted... in the near future," it said.
Khuzestan, which has a large ethnic Sunni Arab community, was a major battleground of the 1980s war with Iraq and it saw unrest in 2005 and 2011, but has since been largely quiet.
Kurdish rebels frequently attack military patrols on the border further north, but attacks on government targets in major cities are rare.
On June 7, 2017 in Tehran, 17 people were killed and dozens wounded in simultaneous attacks on the parliament and on the tomb of revolutionary leader Ayatollah Ruhollah Khomeini -- the first inside Iran claimed by IS.
